/**
 * #      114
 * 名称   二叉树展开为链表
 * 链接   https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list
 * 题解   [945](https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/solution)
 * 通过率 72.0%
 * 难道   中等
 */

